It is known that the hydroformylation reaction can be performed with good results using catalysts which comprise a Group VIII-metal compound which also contains a phosphorus or arsenic moiety. In general, preference is given to the use of phosphorus compounds, especially of trialkyl or triarylphosphines or phosphites as ligands in the catalytic hydroformylation of olefins.
It should be noted, however, that there is a vast difference in reactivity between various olefins under similar reaction conditions using an identical catalytic system. It is also known that the organo-phosphorus ligands may exert a distinct influence on the selectivity of the hydroformylation reaction when the same olefin is applied as the substrate. For instance, it is known from the article by Pruett and Smith (J. Org. Chem., Vol. 34, (1969), No. 2, pp 307-330) that in the hydroformylation of oct-1-ene with trisubstituted phosphorus-containing ligands, an aliphatic substituent gives a lower percentage of straight-chain (or normal) aldehdye than an aromatic substituent. However, the selectivity between various aromatic ligands, phosphines as well as phosphites does not seem to differ markedly. From British Pat. No. 1,325,199 it appears that the hydroformylation of hex-1-ene using a rhodium catalyst modified with various aromatic phosphites gives about the same yield and selectivity whereas the conversion using a catalyst comprising the unsubstituted aromatic phosphite, i.e. triphenylphosphite, is at least 10% higher.
It has now been found that a certain class of olefins which can be regarded as markedly less reactive olefins compared with olefins such as oct-1-ene and hex-1-ene can be hydroformylated at high rates and with good selectivity using Group VIII-metal catalysts modified with specific aromatic phosphites.